A Dear Qubitzers, GR=QM

Well he couldn't say that because all his arguments rest on AdS/CFT, which is not only quantum but stringily quantum. However, if classical GR is the low-energy effective field limit of string theory, he could say that classical GR follows from quantum strings.

I would say his point is more that classical GR actually follows (holographically) from quantum mechanics (without gravity) in a suitable limit. For example, if the quantum mechanics model is some strongly-interacting CFT, you expect the dual theory to be well-described by classical GR physics. He then proposes to simulate a CFT with quantum computers to effectively "test" the corresponding gravity theory.

He also goes beyond classical GR. He points out that the Newton constant G in the dual theory is not necessarily small (it depends on the CFT), so you could actually probe strong-coupling quantum gravity dynamics with such a simulation.

Like many high-energy theorists, I think he overestimates how close we are to doing these simulations on quantum computers.

I would say his point is more that classical GR actually follows (holographically) from quantum mechanics (without gravity) in a suitable limit.

Yes. though if the relationship is really symmetric then saying that one follows from the other seems misleading, more like two sides of the same coin.

He says “If there is anything new here it is the idea that information may pass from a laboratory environment to the degrees of freedom of a physical realization of a CFT, thereby bridging the gap between the lab and the bulk. One can enter the bulk, observe it, and go back to the lab…"

He then proposes to simulate a CFT with quantum computers to effectively "test" the corresponding gravity theory.

Here is where I find it difficult to follow him. It seems to me that a CFT simulation is a simulation, not the real thing. But Susskind says that the simulation IS the real thing. Is he thinking that a simulation on a quantum computer (as opposed to a simulation on a classical computer) is a "real," material implementation of the physics being simulated?

Here is where I find it difficult to follow him. It seems to me that a CFT simulation is a simulation, not the real thing. But Susskind says that the simulation IS the real thing. Is he thinking that a simulation on a quantum computer (as opposed to a simulation on a classical computer) is a "real," material implementation of the physics being simulated?

I suspect he means that due to the computational complexity of the boundary theory vs bulk theory, classical computers are just too slow?

Wether its the real ting that depends what you mean but i also find it strange.

OTOH i dont think we need quantum computers to test this. I rather see the observation that the "bulk representation" has a lower comuputational complexity as the key both to how small systems can "survive" in the chaos. It also explains why an evolutionary selection in favour or space.

The vision i see here
Bulk = observers information
Boundary = observers interaction with the envirroment.

Now consider the evolution of interacting observers. Clearly the difference in complexity of different duals implies a selective pressure that will select our place in the landscape. The selection is a mere race... SLOW coders dont make it... fast coders dominate.

Wether its the real ting that depends what you mean but i also find it strange.

I mean the real thing in a physical sense. I have no problem with the idea that a simulated reality can be real in its own terms, for example from the point of view of sentient observers living in the simulated reality. But here Susskind says "Instead of shells supporting conformal field theories,a more practical alternative might be quantum computers simulating the CFTs," and implies that these quantum computers would have an AdS dual etc. But what physically happens in a computer simulation is electrons moving in semiconductor circuits etc., NOT QCD-like fields, so why should AdS/CFT apply? Therefore I suspect what Susskind has in mind is that what physically happens in a quantum computer (as opposed to a non quantum computer) has a dual.

I mean the real thing in a physical sense. I have no problem with the idea that a simulated reality can be real in its own terms, for example from the point of view of sentient observers living in the simulated reality. But here Susskind says "Instead of shells supporting conformal field theories,a more practical alternative might be quantum computers simulating the CFTs," and implies that these quantum computers would have an AdS dual etc. But what physically happens in a computer simulation is electrons moving in semiconductor circuits etc., NOT QCD-like fields, so why should AdS/CFT apply? Therefore I suspect what Susskind has in mind is that what physically happens in a quantum computer (as opposed to a non quantum computer) has a dual.

I didnt think too much on that part, mainly since I am not primarily seeing this from the stringside, but maybe even just because of that (as I see these from "another side") i find it intriguing that maybe all roads lead to rome after all? Its just that only the fastest road will get to name ithe destination.

But as it see it the only other more "real thing" would be that two entangled qubit registers should then make a wormhole, and thus we can extract information from the bulk QG wormhole but qubot register correlations etc? And if we can make larget set of qubit registers rather than just one qubit, some more interesting things might be inferred from this? I have not thought alot in that direction. I rather envision classical simulations to test the ideas, but due to complexity simulating the real thing is simply impossible. You dont have to think long until its like the hitchhikers galaxy where earth is just a simulator.